The present invention relates generally to a device and method for treating a blockage or stenosis in a vessel of a patient. More specifically, the present invention relates to a device and method for precisely and accurately delivering a dosage of radiation to a vessel to inhibit re-stenosis.
It is well known that many medical complications are caused by a partial or total blockage or stenosis of a blood vessel in a patient. Depending on the location of the stenosis, the patient can experience cardiac arrest, stroke or necrosis of tissues or organs. Commonly, the stenosis is caused by the build-up of artherosclerotic plaque in the intima of the vessel. The plaque typically builds up irregularly in the vessel. As a result of the irregular build-up of plaque, the lumen of the vessel, in most blocked vessels, is not centrally located relative to the external elastic lamina.
Several procedures have been developed to treat stenoses, including angioplasty, stenting, and atherectomy. However, none of these procedures are entirely successful in inhibiting or preventing the re-stenosis of a vessel after the procedure is completed.
Recent studies have demonstrated that radiation may inhibit or prevent re-stenosis in the vessel by inhibiting or preventing the growth of fibrotic cells in the vessel wall, commonly referred to as neointima. The precise target for the radiation in the vessel is currently not known. However, it is believed that the adventitia may be a key source of growth of the neointima. Therefore, it is theorized that the entire vessel, including the adventitia should be treated with radiation.
At least one delivery device has been used for performing intravascular radiation treatment on a treatment site of the vessel. This delivery device utilizes a catheter to position a radiation source in the vessel lumen, adjacent the treatment site. The radiation source is positioned in the vessel lumen and is allowed to emit radiation until the prescribed dosage is released. With this delivery device, the tissue closest to the radiation source receives a larger radiation dosage than the tissue farthest from the radiation source. Subsequently, the radiation source is removed from the vessel lumen.
However, the results obtained using this type of delivery device are not entirely satisfactory. Specifically, because the growth of the plaque inside the vessel is irregular and/or the vessel is curved, the radioactive source is not centered in the vessel relative to the vessel lamina. Thus, depending upon the dosage prescribed, this can result in undertreating certain portions of the vessel and overtreating certain other portions of the vessel. For example, certain portions of the vessel lamina will receive a larger dosage of radiation than other portions of the vessel lamina.
Undertreating with radiation can result in not inhibiting the neointima and, in some instances, can actually result in stimulating smooth muscle cell proliferation and extra-cellular matrix production. Overtreating with radiation can, for example, induce necrosis or an aneurysm. Therefore, it is important to avoid overtreating and/or undertreating of a treatment site of the vessel.
One attempt to solve this problem involves accurately centering the delivery device in the vessel, relative to the vessel lumen. This can be accomplished using a variety of mechanical devices, such as a centering balloon or an expandable mechanical strut. However, these mechanical devices add excessive mass and bulk to the delivery device. This limits the usefulness of the present delivery device to relatively large vessels, i.e., three and one-half millimeters (3.5 mm) or larger and increases the risk of occluding blood flow in the vessel. Moreover, there is a risk that the delivery device will not be accurately centered.
In light of the above, it is an object of the present invention to provide a device and method for delivering a precise dose of radiation to a treatment site within a vessel without centering the delivery device. Another object of the present invention to provide a device and method for delivering a substantially uniform dose of radiation to the vessel lamina and other areas of the vessel. Another object of the present invention is to provide a device which can be used to precisely evaluate the amount and distribution of atherosclerotic plaque in a vessel and which can tailor the treatment in view of the evaluation. Still another object of the present invention is to provide a device and method which is relatively safe and easy to use in curved vessels. Another object of the present invention is to provide a device which can be easily adapted to meet the specific needs of the patient. Still another object of the present invention is to provide a device for accurately providing a treatment plan based upon the configuration of the treatment site of the vessel. Yet another object of the present invention is to provide a device which is relatively simple and inexpensive to manufacture.
The present invention is directed to a device which satisfies these objectives. The device is useful for delivering an asymmetrical dose of radiation to a treatment site of a vessel to treat a stenosis in the vessel. In one embodiment, the device includes an adjuster section adapted to be positioned into the vessel. As provided herein, the adjuster section alters the intensity of a portion of the radiation emitting radially from the radiation source when a portion of the radiation source is positioned in the vessel. In use, the adjuster section partly alters the intensity of radiation directed at where the vessel lamina is the closest. This prevents overtreatment of the vessel.
As used herein, the term xe2x80x9cradiation dose profilexe2x80x9d refers to and means a cross-sectional pattern of energy being delivered to the vessel from a radiation source. A more comprehensive definition of radiation dose profile is provided in the description section.
As used herein, the term xe2x80x9cvessel wallxe2x80x9d refers to and means the structural support of the vessel. For an artery, the vessel wall includes an endothelium, a basement membrane, a vessel intima, an internal elastic lamina, a vessel media, a vessel external elastic lamina (hereinafter xe2x80x9cvessel laminaxe2x80x9d), and a vessel adventitia. For a diseased artery, the vessel wall can also include atherosclerotic plaque which infiltrates the vessel intima and causes stenosis of the vessel.
The adjuster section alters a portion of the radiation emitting radially from the radioactive source so that a radiation dose profile which is substantially asymmetrical and eccentric is delivered to the vessel. With an eccentric, asymmetrical radiation dose profile, more radiation is directed at where the vessel lamina is farthest from the radiation source, while less radiation is delivered to where the vessel lamina is the closest. Thus, a substantially uniform dosage of radiation can be delivered to the vessel lamina at the treatment site, even though the delivery device is not centered in the vessel relative to the vessel lamina.
In one version of the present invention, the adjuster section includes a plurality of spaced apart conductor coils which create a magnetic field proximate to the radiation source. Depending upon the direction of current through each conductor coil, each coil either attenuates or potentiates the charged particle radiation which emits from the radiation source. Further, the amount of attenuating or potentiating for each conductor coil depends upon the magnitude of the current in each conductor coil. Thus, the radiation dose profile relative to the radiation source can be specifically tailored for a particular vessel by adjusting the magnitude and direction of current in each conductor coil.
Typically, conductor coils are attached to a catheter and spaced apart radially around the catheter. Additionally, the conductor coils can be spaced apart longitudinally along the catheter. This feature allows the radiation dose profile along a longitudinal axis of the radiation source to be modified so that the radiation dose profile along the radiation source is varied. Thus, the radiation dose delivered to the vessel can be accurately tailored to suit the shape of a treatment site.
In another version, the adjuster section can be an attenuator section which includes an attenuator material. The attenuator material at least partly diminishes the intensity of the radiation which emits radially from the radiation source. The attenuator material is typically a relatively dense material having a relatively high atomic number. Preferably, the attenuator material is also bio-compatible and safe for use in surgery. Materials such as gold, platinum, and tantalum can be used. Additionally, the attenuator section can be divided into a plurality of spaced apart, attenuator segments, so that the adjuster section is more flexible and easier to move through a curved vessel.
Importantly, the design of the adjuster section determines the shape of the radiation dose profile which is delivered to the vessel. Thus, the present invention can be utilized to provide an accurate dose of radiation to a treatment site.
As used herein, the phrase xe2x80x9cconfiguration of the attenuator sectionxe2x80x9d shall mean the size, shape, thickness, and material utilized in the attenuator section. Also as used herein the phrase xe2x80x9cconfiguration of the vessel wallxe2x80x9d shall mean the size and shape of the vessel wall at the treatment site, including the positioning of the vessel lamina relative to the vessel lumen, and the shape and size of the atherosclerotic plaque.
Preferably, the device also includes an imager which is secured proximate to the adjuster section. The imager allows for substantially real time images of the vessel prior to and during treatment with radiation. This embodiment is preferred so that the position of the adjuster section in the vessel can be constantly monitored during treatment with radiation. This allows the doctor performing the procedure to correct deficiencies which may arise in the positioning of the adjuster section.
The invention is also a method for delivering radiation from a radiation source to a treatment site of a vessel. The method includes the steps of positioning the radiation source in the vessel and creating a magnetic field within the vessel, so that the radiation source delivers a radiation dose profile in the vessel relative to the radiation source which is substantially asymmetrical.
Further, the invention can also include the step of altering the radiation emitting from the radiation source, so that the radiation dose profile also varies along the longitudinal axis of the radiation source. This feature allows the dose of radiation delivered to the treatment site to be accurately tailored longitudinally to suit the needs of the patient.
In alternate embodiments, some of the features outlined above can be directly incorporated into the radiation source and/or the radiation source can be a stent. Further, a controller can be utilized which receives the images from the imager and provides a treatment plan for the treatment site.
It is important to recognize that with the present invention, the vessel receives a radiation dose profile which is substantially asymmetrical relative to the radiation source. Therefore, the radiation source is able to deliver a substantially uniform dose to the vessel lamina, even though the radiation source is not centered relative to the vessel lamina. Further, the radiation delivered to the vessel can be specifically tailored to suit the configuration of the vessel wall at the treatment site.